The overall objective of this program is to develop nanostructured porous silicon as neural electrode materials with enhanced biocompatibility, in particular for novel hybrid silicon/ceramic multi-site neural recording electrode arrays. We have previously shown that the pure ceramic-based multi-site neural electrode arrays can consistently record multiple single neuron activity chronically for up to six weeks. These results are similar to microwire electrodes and better than other thin film electrodes. However, in order for any electrode system to act as neural interface components of neural prosthetic devices, the electrode will be required to record consistently for many years. Preliminary studies have shown that by introducing widely varying porosity into silicon, its behavior can be tuned from that of a relatively bio-inert material to one that is bioactive, and even resorbable. In this proposal, we plan to investigate two types of semi-flexible nanostructured hybrid silicon/ceramic neural electrodes. In one type, the electrode material will be based solely on nanostructured porous silicon formed electrochemically on a thin Si substrate. In the second type of electrode, an additional ultra-thin layer of ceramic material will be formed conformally onto the nanostructured porous silicon using a special deposition process. The latter structure will allow us to directly compare the performance of electrodes with essentially nanostmctured ceramic surface to conventional ceramic-based devices. In Phase I, the efficacy of nanostructured porous silicon neural electrodes will be evaluated in vivo using rat brain model. The neural tissue will be evaluated using histology methods to look for neural damage near the site of implantation and study the growth of neurons into the porous silicon electrodes. To promote neural growth at the electrode/tissue interface and for better contact of the recording sites on the array with neurons, we will test the ability of the porous silicon to deliver neurotrophic molecules. In Phase II, upon optimizing the parameters for nanostructured porous silicon electrodes, Spire and its collaborators will design, fabricate and test in vivo performance of a two dimensional array of porous silicon-based neural electrodes for chronic, long-term (greater than 6 months) multi-site recording.